The electrical contact construction as embodied in the subject invention is of the type as illustrated and described in applicant's prior issued U.S. Pat. No. 3,435,168.
In the aforesaid U.S. Pat. No. 3,435,168, an electrical contact is disclosed that is of the plunger-type and that is generally for use in testing of printed circuit boards on test fixtures. Although not disclosed in the prior mentioned patent, the spring-loaded test probes as shown and described in the patent are mounted in a test fixture and a plurality of corresponding contacts are located in an array on a printed circuit board under test. When the board is placed in the test fixture, electrical contact is made between the contacts which define the test probes and the circuit of the printed circuit board for purposes of carrying out the testing procedure.
As shown in U.S. Pat. No. 3,435,168, the electrical contact illustrated and described therein generally includes an elongated tubular member in which a plunger is located, the plunger being disposed outwardly in a biased position by a contact spring. A ball member is also located within the tubular member and cooperates with the spring to normally urge the plunger outwardly of the tubular member. In order to prevent the plunger from being expelled from the tubular member under pressure of the spring, a plurality of indentations or dimples are formed in the tubular member and are engageable by an enlarged portion of the plunger. Although the dimples were not disclosed in the prior known construction as having sharp inner corners, the dimples were formed such that the inwardly directed projections produced by the dimples were generally semi-spherical and only point contact was made by engagement of the plunger portion therewith. This sometimes resulted in the plunger member riding over the dimples and becoming lodged or wedged therebetween and the wall of the tubular member, thereby preventing the contact from operating effectively during tests. Even the bevel as formed on the end of the plunger member was not always effective in preventing the plunger from becoming snared or wedged on one of the dimple projections as formed in the wall of the tubular member.
In some instances and in particular when the diameter of the tubular member was relatively large, an annular ring was formed in the tubular member for defining the plunger stop. Such a ring defined a continuous shoulder which was effective for receiving the plunger portion thereagainst. However, the formation of the annular ring sometimes weakened the wall of the tubular members which on occasion caused the tubular member to snap apart during use.
It is the purpose of the subject invention to avoid the attendent difficulties as experienced in the so-called retaining means of the electrical contact as disclosed in the aforesaid U.S. Pat. No. 3,435,168 and as further discussed above and to provide an effective but inexpensive stop for the contact plunger.